when i start facebook or youtube, a dialogue box appears above the page that asks for enabling the javascript for better performance.
I use Noscript and it shows that fbcdn.net for facebook is blocked and due to that i am unable to open any thing on it. but the moment i allow it, my firefox crashes.
Same thing is with youtube, when i intend to watch any video it crashes.

when i start facebook or youtube, a dialogue box appears above the page that asks for enabling the javascript for better performance.
I use Noscript and it shows that fbcdn.net for facebook is blocked and due to that i am unable to open any thing on it. but the moment i allow it, my firefox crashes.
Same thing is with youtube, when i intend to watch any video it crashes.

See:
*http://kb.mozillazine.org/Firefox_crashes
*https://support.mozilla.org/kb/Firefox+crashes
Do the crashes still occur in Safe mode?
*https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

This solved my problem.
1. Close Firefox completely
2. Click on Start | Run | Type “firefox.exe –p” without quotes
3. Click OK
4. Click on Create Profile | Choose the user Profile Window.
5. In Create Profile Wizard click on Next.
6. Type the name in New Profile Name and Click on Finish.
7. Uncheck Don’t ask at Startup and click on Start Firefox.
This newly created user profile would appear whenever you start Firefox web browser. If you do not want to see this Window quite often, uncheck this Window.
Read more: http://digitaljournal.com/blog/15416#ixzz2Mmamk3hJ